Within the scope of typical operating methods, the actual torque actually delivered by the internal combustion engine is ascertained from various performance quantities of the internal combustion engine, such as an injection duration and an injection pressure at which the fuel is injected into the combustion chamber. Reliable operation of the internal combustion engine is monitored with the aid of this actual torque. If the actual torque ascertained in the way described above exceeds a predefinable threshold value, for example, an error may be entered in a control unit which controls the internal combustion engine, or the injection device may even be deactivated via a separate shutdown path provided for this purpose. For example, a permissible torque which is derived from a setpoint torque used for activating the internal combustion engine, for example, is also used as the threshold value or comparison value for monitoring the actual torque.
A comparable calculation of the actual torque is discussed, for example, in German patent document DE 103 00 194 A1, which is hereby declared to be part of the disclosure of the present description, and therefore is incorporated by reference in the present application.
However, the typical operating methods are sometimes very inaccurate with regard to ascertaining the actual torque which, inter alia, is to be attributed to a large scatter of the individual properties of the injection devices. In this context, for example, a diameter of a nozzle opening and other characteristic physical variables which are capable of influencing the function of the injection device, as well as aging behavior and the like, for example, are understood as individual properties of the injection device.
This scattering is mostly related to manufacturing and in the present case influences, inter alia, the relationship between the injection duration, the injection pressure, and a fuel quantity actually injected into the combustion chamber, of which the actual torque is in turn a function.
Accordingly, it is the object of the present invention to refine an operating method according to the definition of the species in the main claim as well as a control unit and a computer program for a control unit in such way that more reliable ascertainment of the actual torque and thus improved monitoring of the internal combustion engine are possible.
This object is achieved according to the present invention for an operating method of the type cited at the beginning in that the individual properties of the injection device are taken into consideration when ascertaining the actual torque.